1. Field of the Invention
This invention relates to a hand-held air blower device, and is particularly useful in accelerating the drying of intermediate and final coats of water-borne coatings for example during the re-painting of road vehicles, as described in my U.S. patent application Ser. No. 08/055,012, which is hereby incorporated by reference. As explained in the above identified Patent Application, the use of water-borne paints instead of solvent-based paints for vehicle re-spraying has overcome environmental and other problems, but has introduced the problem of removing water from the paint once it has been sprayed. Blowing air at water-based coatings tends to cause the formation of a skin on the outer surface which then severely limits the proper loss of water from within the film. This has adverse consequences on the appearance of film, since shrinkage of the film can be uneven and flake control in metallic or mica flake containing films deteriorates. A further disadvantage of air blowing systems has been the disturbance of dust from adjacent surfaces, which contaminates the coating.
2. Description of the Prior Art
Heating vehicles in a hot air blown kiln to cure the base coating is of course a conventional process, as disclosed for example in FR-A-2029314, where high temperatures such as 200.degree. C. are proposed. Indeed, infrared radiative heating has been proposed for accelerating secondary coatings preparatory to a top coating. Heating in this way is not only expensive for a motor vehicle re-spray process but is also of course impractical for an assembled vehicle which would be damaged by the heat.
In the Patent Application referred to above, I disclose as my invention the method of forcing evaporation of solvent such as water from a coating on a pre-defined surface of a panel by directing a jet of air from an air supply held at a predetermined distance from the panel towards one edge region of the panel, the jet being substantially narrower, when it reaches the panel edge region than the length of the panel edge and the jet being inclined to the plane of the panel such that the air from the jet is entrained by the panel in a spreading, predominantly laminar flow across the panel surface over that edge region and from that edge region to all the other edges thereof, thereby inducing such laminar flow over substantially the whole surface and replacing vapor-laden air closely adjacent the surface with fresh air to accelerate drying. The use of an essentially local air supply allows the position and direction of the air jet to be controlled so as to optimize the drying effect of the air, and so as to avoid disturbing any dust which may be present on adjacent surfaces. While the flow velocity of the air jet may be 1-2 m/sec. as it reaches and travels along the panel surface, there is no need to increase the usual flow rate of drying air which may be moving in bulk elsewhere, e.g. from ceiling to floor in a booth. This also avoids dust disturbance. This method is particularly energy efficient and it is surprisingly effective in drying panels such as vehicle doors and bonnets.
The preferred form of air supply is one which supplies a jet of air at a flow velocity substantially greater than any external air flow, such as the bulk movement of air from the ceiling to the floor of a paint booth. The preferred form of air supplier is of the "air mover" type, which uses a source of high-pressure air to entrain atmospheric air taken from the exterior, so that the air mover provides an outlet jet which is a combination of air from the high pressure source and air from the exterior. The principle of using a jet of high pressure air to entrain the flow of lower pressure air is known for example from U.S. Pat. No. 3,942,724 (Mocarski) which discloses a nozzle with high and low pressure air inlets.